1. What is BSA in Psoriasis?

Body Surface Area (BSA) affected by psoriasis is a key measure of disease severity. It represents the percentage of total skin surface covered by psoriatic lesions. The palm method (1 palm ≈ 1% BSA) is a practical clinical tool for estimation.

2. How to Calculate BSA for Psoriasis

The calculator uses the palm method combined with rule of nines for larger areas:

Where:

• 1 palm = approximately 1% of total BSA
• Arm = 9% of total BSA
• Leg = 18% of total BSA
• Chest or Back = 18% each

Explanation: The patient's palm (including fingers) represents about 1% of their total body surface area. For larger affected areas, the "rule of nines" provides standardized estimates.

3. Importance of BSA Measurement

Details: BSA assessment helps classify psoriasis severity (mild: <3%, moderate: 3-10%, severe: >10%), guide treatment decisions, and monitor treatment response over time.

4. Using the Calculator

Tips: Count how many palm-sized areas are affected (1 palm ≈ 1%). For larger contiguous areas, select the appropriate body part from the dropdown. The calculator sums these values automatically.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the palm method?
A: It's a clinical estimate. Actual palm size varies, but it's sufficiently accurate for treatment decisions. For research, more precise methods may be used.

Q2: What if lesions are smaller than palm size?
A: Combine smaller lesions to estimate palm equivalents (e.g., ten lesions each 10% of palm size = 1 palm).

Q3: How does BSA relate to PASI score?
A: PASI incorporates BSA but also considers erythema, thickness, and scaling. BSA alone is simpler but less comprehensive.

Q4: Should nails be included in BSA?
A: Nail psoriasis is typically assessed separately, though severe nail involvement may influence treatment decisions.

Q5: How often should BSA be reassessed?
A: During treatment initiation, assess every 3 months. For stable patients, every 6-12 months may be sufficient.